JPH11269261A - Preparation of polytetramethylene ether glycol - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an industrially advantageous preparation process wherein a polytetramethylene ether glycol with a narrow molecular weight distribution is prepared using 1,4-butanediol or an acetic acid ester thereof as a starting material. SOLUTION: A preparation process of a polytetramethylene ether glycol comprises steps wherein 1,4-butanediol and/or an acetic acid ester of 1,4- butanediol is cyclized in the presence of an acid catalyst to prepare tetrahydrofuran and the obtained tetrahydrofuran is ring-opening polymerized in the presence of an acidic catalyst to prepare a polytetramethylene ether glycol. Here, an oligomer thereof is separated form the obtained polytetramethylene ether glycol and recycled in the preparation process of tetrahydrofuran.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing polytetramethylene ether glycol (abbreviated as PTMG). More specifically, the present invention relates to a method for economically producing PTMG having a narrow molecular weight distribution. PTMG is used as a raw material for polyester resins, polyurethane resins and the like.

[0002]

2. Description of the Related Art There are various methods for producing PTMG. Usually, PTMG is produced by ring-opening polymerization of tetrahydrofuran (abbreviated as THF). As one of industrial processes, THF is subjected to ring-opening polymerization in the presence of a carboxylic anhydride, for example, acetic anhydride and a solid acid catalyst, to obtain a dicarboxylic acid ester of polytetramethylene ether glycol (PTM).
E) and then transesterification with a lower alcohol such as methanol to produce PTMG.

[0003] PTMG is a polymer, which is a mixture of many molecules having different degrees of polymerization and has a molecular weight distribution. Recently, PTMG having a narrow molecular weight distribution has been used as an industrial product.
Is required. Known methods for narrowing the molecular weight distribution include a method of separating PTMG with a solvent such as a water-methanol mixture, a method of separating PTMG oligomers by molecular distillation, and a method of combining these (for example, USP 5,282). 929, JP-A-Hei 1
-92221).

It is known that the separated oligomer can be reused as THF when depolymerized in the presence of an acid catalyst. However, these methods require an apparatus for PTMG solvent separation, oligomer recovery, and depolymerization, and are not necessarily industrially satisfactory.

[0005]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides an industrially advantageous PTMG by separating its oligomer from PTMG to obtain a product having a narrow molecular weight distribution and economically recycling the recovered oligomer. It is an object of the present invention to provide a production method of

[0006]

Means for Solving the Problems The present inventors have made THF dehydrocyclization or deacetic cyclization using 1,4-butanediol (hereinafter abbreviated as 1,4BG) and / or 1,4-BG acetate as a raw material. Then, THF is subjected to ring-opening polymerization in the presence of an acidic catalyst to produce polytetramethylene ether glycol (hereinafter abbreviated as PTMG), and oligomers in the PTMG are removed by a method such as distillation to obtain a molecular weight of PTMG. In the process of producing PTMG with improved distribution, an effective use of the separated oligomer was examined. However, in the THF production process, unreacted 1,4B
As a result of paying attention to the fact that acetate esters of G or 1,4BG (hereinafter collectively referred to as recovered 1,4BG) are collected and reused as a raw material of THF, the recovered 1,4BG contained It was found that polyether-type high-boiling substances condensed between the molecules existed, and it was found that the oligomer separated from PTMG could be reused as THF if mixed with 1,4BG recovered and subjected to a THF production reaction. . Even more surprisingly, in the THF conversion reaction, there is an equilibrium between the high-boiling reaction by intermolecular condensation and the THF-forming reaction by depolymerization of the high-boiling material. By adding PTMG oligomers, THF can be efficiently converted. It has been found that it can be generated. The present invention has been achieved based on such novel findings, and the gist of the present invention is to cyclize 1,4-butanediol and / or 1,4-butanediol acetate in the presence of an acid catalyst to form tetrahydrofuran. A method for producing polytetramethylene ether glycol, comprising a step of producing the polytetramethylene ether glycol by subjecting the obtained tetrahydrofuran to ring-opening polymerization in the presence of an acidic catalyst to produce polytetramethylene ether glycol. The present invention provides a method for producing polytetramethylene ether glycol, comprising separating an oligomer of polytetramethylene ether glycol from methylene ether glycol and circulating the oligomer in a tetrahydrofuran production step. Hereinafter, the present invention will be described in detail.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a THF production process for producing THF as a raw material of PTMG, 1,4
BG or 1,4BG mono- or diacetate or a mixture thereof is used. When an acetic ester is used, it is preferable to add water because acetic acid generated together with THF inhibits a THF generation reaction. The THF formation reaction is usually performed at a reaction temperature of 50 ° C. to 100 ° C. using a sulfonic acid type strongly acidic cation exchange resin as a catalyst. When the temperature is low, the THF generation rate is low, and when the temperature is high, the life of the ion exchange resin is shortened.
C is preferred. The pressure is preferably in the range of normal pressure to 1 MPa, but a slight pressure is preferably used in order to suppress the boiling of the formed THF. The reaction solution withdrawn from the THF production reactor was THF, water, unreacted 1,4B
Since it contains G and / or 1,4BG acetate and some high-boiling substances, and in some cases, acetic acid, unreacted substances are separated and recovered by means such as distillation, and recycled and reused in a THF production reactor. On the other hand, the product containing THF is purified by means such as distillation to obtain THF substantially free of water, and if necessary, high boiling substances that may be contained are further separated by distillation, and preferably Used as a raw material for PTMG production.

Various methods for producing PTMG are known. Among them, a dicarboxylic acid ester of PTMG obtained by ring-opening polymerization of THF in the presence of an acid catalyst and a carboxylic acid, for example, acetic anhydride, is converted to a lower alcohol. A method of producing by transesterification is preferable. This manufacturing method will be described in more detail. The acid catalyst to be used is not particularly limited, and a known one can be used. Examples thereof include solid acid catalysts such as super-strong acidic cation exchange resin described in JP-B-61-11969, bleaching earth described in JP-B-62-19452, and zeolite described in JP-A-7-228684. A liquid acid such as perchloric acid can be used, but this is industrially disadvantageous because the process of neutralizing and / or separating the acid after ring-opening polymerization becomes complicated. It is preferable to use a solid acid catalyst because the catalyst can be easily separated. The solid acid catalyst can be used in either a suspension bed or a fixed bed. However, it is particularly preferable to use a solid acid catalyst in a fixed bed flow reaction because there is no need to separately perform a catalyst separation operation.

The reaction conditions vary depending on the desired molecular weight of PTMG and the type of acid catalyst used. When acetic anhydride is used as the carboxylic acid, the concentration of the acid catalyst in the reaction solution is usually 0.1 to 50% by weight. %, Acetic anhydride at a concentration of about 0.1 to 30% by weight. The reaction temperature is usually in the range of -20 to 150 ° C, and the reaction time is usually selected in the range of 0.5 to 10 hours. The polymerization reaction solution obtained was a PTMG dicarboxylic acid ester (PTM
E) and unreacted raw materials and the like, so that unreacted THF and acetic anhydride are usually distilled off under normal pressure or reduced pressure. The distilled off THF and acetic anhydride can be purified, if necessary, and reused for ring-opening polymerization of THF or other uses.

Next, PTMG is produced by transesterification from PTME from which unreacted raw materials have been removed. The method of transesterification, the catalyst used, the alcohol, and the like are not particularly limited, and known ones can be used. For example, Japanese Patent Publication No. 61-11969 discloses that alcohols having 1 carbon atom
A process using an alkanol of -4 and an oxide, hydroxide or alkoxide of calcium, strontium, barium or magnesium as a catalyst is disclosed. In addition, Japanese Patent Publication No. 1-147686 describes that the number of carbon atoms is 1-1.
A method is disclosed in which a reaction is carried out using 0 linear and branched alcohols and calcium oxide or calcium hydroxide as a catalyst in the presence of 0.01 to 0.1% of water as required. Among these, it is preferable to use a lower (C1-4) alkanol as the alcohol and use a calcium oxide or hydroxide as a catalyst.

The reaction conditions are not particularly limited.
The catalyst is used in an amount of 0.001 to 1% by weight and the lower alcohol is used in an amount of 5 to 30 times by mole based on ME. The reaction is usually carried out at the boiling point of the lower alcohol, but can be carried out at a higher temperature by applying pressure. The reaction may be performed in the presence of a small amount of water. The reaction may be carried out batchwise or continuously, or a reactor having two or more stages may be used. It is preferable that the by-produced acetate of lower alcohol be distilled off during the reaction in order to push out the reaction.

The obtained PTMG is subjected to neutralization, filtration and distillation of lower alcohol by a known method, if necessary. The distilled lower alcohol may be purified as necessary and reused for transesterification or other uses. Usually, industrially, the number average molecular weight is 500 by the above method.
Up to 3000 PTMG can be obtained and used as a raw material for polyurethane elastic fiber, polyurethane elastomer or polyester elastomer.

The method of producing PTMG from THF is not limited to the above-mentioned method, and known methods such as a method of hydrolyzing PTME with an alkaline catalyst and a method of ring-opening polymerization of THF in the presence of a fluorosulfonic acid catalyst, etc. Can be adopted. The PTMG thus obtained contains several percent of dimers to about 10-mers of oligomers. Oligomers are said to have an adverse effect on the physical properties of elastic fibers and elastomers, and PTMG with less oligomers is desired. As a method for removing the oligomer, methods such as distillation, ultrafiltration, and separation with water-methanol are known. Among them, a method using distillation using a thin film evaporator or a molecular distillation apparatus is simple.
The distillation is carried out under a high vacuum of 5 torr (666.5 Pa) or less at a temperature of 250 ° C. to 350 ° C. Usually, oligomers having a molecular weight of pentamer or less are separated as a distillate. PTMG with reduced oligomers is obtained as a bottom liquid, which is suitably used as a raw material for polyurethane resin or fiber.

The separated oligomer can be used as a raw material for special applications in some cases. However, in the method of the present invention, the separated oligomer is recycled to a THF production step and is used again as a THF production raw material. The reaction conditions of the reactor for producing THF from 1,4BG and its acetate ester are the same as the depolymerization conditions of the oligomer, and the oligomer is depolymerized in this reactor to produce THF. Therefore, there is no need to install new equipment for oligomer treatment. or,
The addition of the oligomer promotes the equilibrium of the THF production reaction in the direction of the THF production.
The production of MG can be performed.

[0015]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. “%” And “parts” mean “% by weight” and “parts by weight” unless otherwise specified.

Example 1 (THF production process) 1-hydroxy-4-acetoxybutane obtained by hydrolyzing 1,4-diacetoxybutane 58%, 1,4-diacetoxybutane 27%, 1,4
-An aqueous liquid containing 9% of BG is introduced into a THF production reactor filled with a sulfonic acid type strongly acidic cation exchange resin together with an unreacted substance recovered from a high boiling separation column described later and an oligomer separated from PTMG. Then, the reaction was carried out at a temperature of 80 ° C. and a residence time of 6 hours. Since the reaction solution contains THF, acetic acid, water and unreacted substances, it is introduced into a high-boiling separation column,
Unreacted material was collected as bottoms and circulated to the THF reactor. The high boiling separation column has a top pressure of 290 torr (0.39 torr).
MPa), operating at a bottom temperature of 185 ° C. and a reflux ratio of 0.3,
A distillate containing 67% of THF, 22% of acetic acid, and 10% of water was obtained from the top of the column, and supplied to an acetic acid separation column together with a distillate of a dehydration column described below. A bottom product containing acetic acid and water as main components was withdrawn from the bottom of the acetic acid separation tower, and 5.9% of water and THF94.
An azeotrope consisting of 0% was distilled off. The azeotrope is
Distillation is conducted in a 14-stage theoretical dehydration column operated at a pressure of 0.83 MPa · G and a reflux ratio of 0.3, and THF containing 13% of water is distilled from the top of the column, supplied to an acetic acid separation column, and removed THF having a water content of 50 ppm or less was obtained as a liquid. The bottom liquid was supplied to a THF purification column operated at normal pressure and a reflux ratio of 0.6, and THF having a purity of 99.9% or more was distilled off from the top of the column and supplied to a PTMG production process.

(PTMG manufacturing process) THF 2000 parts,
The reaction was carried out at 40 ° C. for 8 hours in a reactor equipped with a stirrer using 100 parts of zirconia-silica powder obtained by calcining 332 parts of acetic anhydride at 800 ° C. as a catalyst. After the completion of the reaction, the catalyst was filtered, and unreacted THF and acetic anhydride were distilled off from the colorless polymerization solution under reduced pressure to obtain PTMG diacetate. TH
The conversion of F was 55%. When the obtained diacetate of PTMG was analyzed by gel permeation chromatography (GPC) using polyethylene glycol as a standard, the number average molecular weight (Mn) was 2000 and the molecular weight distribution (Mw / Mn) was 2.1. there were.

Next, this PTMG diacetate 10
00 parts and methanol 1000 parts, calcium hydroxide 1
Part of the mixture was charged into a reactor equipped with a distillation column having 20 theoretical plates, and the mixture was boiled and heated for 6 hours with stirring, while distilling an azeotropic mixture of methanol / methyl acetate from the top of the distillation column. Replaced. The azeotrope obtained is 88
Department. When the liquid in the reactor was analyzed by an infrared absorption spectrum, the amount of the remaining ester was below the detection limit.

After cooling, the reaction solution was filtered through a pressure filter equipped with a 1 μm filter to remove calcium hydroxide, thereby obtaining 1910 parts of a colorless and transparent filtrate. About 1 in the filtrate
Since 0 ppm of calcium hydroxide was dissolved, sulfonic acid type strongly acidic cation exchange resin Diaion SK1 was used.
The solution was passed through a 30 ° C. adsorption tower filled with BH (trademark; manufactured by Mitsubishi Chemical Corporation) to remove dissolved calcium hydroxide. The calcium in the solution subjected to the adsorption treatment was analyzed and found to be below the detection limit. Processing solution After removing most of the methanol under normal pressure using an evaporator, PTMG which is continuously treated in a thin film evaporator operated at a heating medium temperature of 250 ° C. under a reduced pressure of 10 torr (1333 Pa) and is substantially free of methanol
870 parts were obtained. The obtained PTMG was analyzed by GPC using polyethylene glycol as a standard. As a result, the molecular weight (Mn) was 1920 and Mw / Mn was 2.15.

This PTMG is added at 0.5 torr (66.7).
The oligomer is distilled off using a thin film evaporator operated at a heating medium temperature of 250 ° C. under a reduced pressure of Pa), and the molecular weight (Mn) is reduced.
1995 PTMG was obtained as bottoms. Mw / Mn was 2.0. The distillate of the oligomer was 0.8%, and the whole amount was circulated to the THF production reactor and reused as a THF production raw material.

[0021]

According to the method of the present invention, PTMG produced from 1,4-BG and / or its acetate is used as a raw material.
To obtain PTMG with a narrow molecular weight distribution, and to circulate the separated oligomer to the THF production process and reuse it as a raw material for THF production. , And the efficiency of the THF production reaction can be improved, and PTMG can be produced industrially and extremely advantageously by an economical method.

Claims (2)

[Claims] Claims: 1. 1,4-butanediol and / or 1,4-butanediol
A step of producing tetrahydrofuran by cyclizing an acetate of 4-butanediol in the presence of an acid catalyst, and a step of producing polytetramethylene ether glycol by ring-opening polymerization of the obtained tetrahydrofuran in the presence of an acidic catalyst. , A method for producing polytetramethylene ether glycol, wherein an oligomer of tetramethylene ether glycol is separated from the obtained polytetramethylene ether glycol and circulated to a tetrahydrofuran production step. Method. 2. The step of producing polytetramethylene ether glycol by ring-opening polymerization of tetrahydrofuran,
The process is characterized by reacting tetrahydrofuran with a solid acid catalyst in the presence of carboxylic anhydride to obtain polytetramethylene ether glycol diacetate, and transesterifying this with a lower alcohol to produce polytetramethylene ether glycol. The method for producing polytetramethylene ether glycol according to claim 1, wherein